[IRBuilder] Remove commented out include.

Looks like this was left over during some include optimizations. Remove
it.

Author: fhahn

llvm/include/llvm/IR/IRBuilder.h

@@ -25,7 +25,6 @@
 #include "llvm/IR/ConstantFolder.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
-//#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/FPEnv.h"